The present invention relates to extremely accurate measuring devices and in particular to a calibration device for such devices.
Known long calibration device designs include a header including a central low thermal expansion or contraction core, and stiff spacers to provide a neutral bending plane to the physical center line of the device. Even with the inclusion of the stiff spacers, the neutral bending plane of the known long calibration device is shifted somewhat below the centroid of the measuring axis when the long calibration devices are moved between a vertical and horizontal orientation and several intermediate positions, introducing a very small error due to the deflection caused by the force of gravity acting on the long calibration device. For ordinary calibration applications, this very small error is minute and unimportant because the overall structure is so rigid. Unfortunately, even this minute error is not acceptable when very high precision measurements are required.
One solution to the deflection is to add four structural sheets residing below a central shaft of the long calibration device, with two of the four sheets oriented at 180 degrees to the other two sheets. This solution is not generally used because it doubles the bulkiness of the overall device. Thus, a new design is needed to provide where high precision measurements are required.
Further, the accuracy of long calibration devices has always been a major problem. The accuracy of the actual calibration has been suspect, due to serious errors due to bending from the force of gravity and their temperature sensitivity. Serious change in length due to deflections of the artifact, when its orientation is changed from vertical to horizontal, is a major short coming of conventional very long calibration devices. Thus, a need remains for a long calibration device not affected by orientation or temperature.